A constant velocity universal joint which is to be incorporated into a power transmission mechanism of, for example, automobiles and various industrial machines receives a boot (boot for a constant velocity universal joint) mounted thereto for the purpose of preventing entry of foreign matters such as dusts into the joint or preventing leakage of grease sealed in the joint.
FIG. 10 is an illustration of a drive shaft. The drive shaft is obtained by connecting a fixed type constant velocity universal joint 1 and a plunging type constant velocity universal joint 2 to each other with a shaft 30. In the illustrated example, a Barfield-type constant velocity universal joint is used as the fixed type constant velocity universal joint 1, and a tripod type constant velocity universal joint is used as the plunging type constant velocity universal joint 2.
The fixed type constant velocity universal joint 1 includes an outer joint member 15, an inner joint member 18, a plurality of balls 19, and a cage 20. The outer joint member 15 includes a radially inner surface 14 having a plurality of tracks 13 extending in an axial direction. The inner joint member 18 includes a radially outer surface 17 having a plurality of tracks 16 extending in the axial direction. The plurality of balls 19 are interposed between the tracks 13 of the outer joint member 15 and the tracks 16 of the inner joint member 18 to transmit torque. The cage 20 is interposed between the radially inner surface 14 of the outer joint member 15 and the radially outer surface 17 of the inner joint member 18 to retain the balls 19.
The plunging type constant velocity universal joint 2 includes an outer joint member 22, a tripod member 24, and rollers 25. The outer joint member 22 has three grooves 21 extending in an axis direction on an inner periphery, and roller guide surfaces 21a opposed to each other are formed on inner walls of the grooves 21. The tripod member 24 includes three journals 23 protruding in a radial direction. The rollers 25 each serving as a torque transmission unit are supported on the journals 23 so as to be rotatable and are inserted to the grooves 21 of the outer joint member 22 so as to be rollable. In this case, the rollers 25 are externally fitted onto radially outer surfaces of the journals 23 through intermediation of a plurality of rollers 26 which are arranged along a circumferential direction. The tripod member 24 includes a boss portion 27 and the journals 23 extending in a radial direction from the boss portion 27.
The shaft 30 has male splines 30a and 30b formed at both end portions of the shaft 30. One male spline 30a is fitted into the inner joint member 18 of the fixed type constant velocity universal joint 1, and another male spline 30b is fitted into the tripod member 24 of the plunging type constant velocity universal joint 2. A female spline 34 is formed in an axial center hole 33 of the inner joint member 18, and the one male spline 30a of the shaft 30 is fitted into the axial center hole 33 of the inner joint member 18 and is brought into mesh with the female spline 34. Further, the another male spline 30b of the shaft 30 is fitted into an axial center hole 35 of the boss portion 27 of the tripod member 24 and is brought into mesh with a female spline 36 of the axial center hole 35.
A boot 40A configured to seal an opening portion of the outer joint member 15 is provided to the fixed type constant velocity universal joint 1. A boot 40B configured to seal an opening portion of the outer joint member 22 is provided to the plunging type constant velocity universal joint 2. Each of the boots 40A and 40B includes a large-diameter end portion 40a, a small-diameter end portion 40b, and a bellows portion 40c which connects the large-diameter end portion 40a and the small-diameter end portion 40b to each other. The large-diameter end portions 40a of the boots 40A and 40B are fastened and fixed by fastening clamps 42A and 42B at opening ends of the outer joint members 15 and 22, respectively. The small-diameter end portions 40b of the boots 40A and 40B are fastened and fixed by fastening clamps 43A and 43B at predetermined portions of the shaft, respectively.
Incidentally, the constant velocity universal joint has a function of rotating while taking an operating angle or a function of rotating while sliding in the axial direction. The boot is flexibly deformed so as to follow the actions of the constant velocity universal joint. Further, the constant velocity universal joint may be, for example, of a type which is capable of taking a large operating angle of equal to or more than θ=45 degrees (Rzeppa type or Barfield type) or a type which is not capable of taking a considerably large angle but includes a mechanism configured to slide in an axial direction of the constant velocity universal joint (double-offset type, tripod type, or cross-groove type). Various mounting structures for the boot of such type have hitherto been proposed (see Patent Literature 1 to Patent Literature 6).
According to Patent Literature 1, a clamp groove is formed in an outer periphery of a mounting portion (fixing portion) of a boot. Dimensional and positional relationships are defined for projections and groove portions of a mating member (outer joint member or shaft), the boot fixing portion, and a clamp so as to cause the projections of the mating member to bite into the boot fixing portion, thereby improving sealability.
According to Patent Literature 2, a plurality of projections are formed on a boot receiving portion of a shaft, and a shaft mounting portion of a boot is fastened by a fastening clamp so that at least one of the projections has a compression set amount which is different from those of other projections.
According to Patent Literature 3, a pair of projections are formed on a boot receiving portion of a shaft, and a projection which is to be brought into press contact with the shaft is formed on a shaft mounting portion of a boot at a portion corresponding to a position between the pair of projections.
According to Patent Literature 4, a pair of projections are formed on a boot receiving portion of a shaft, and a recessed groove configured to retain lubricant delivered from an inside of a joint is formed on an inner side with respect to the projection formed on a boot inner side.
According to Patent Literature 5, an annular groove is formed in a boot receiving portion of a shaft, and a projection which is to be fitted into the annular groove is formed in an inner peripheral surface of a mounting portion of a boot. An interference between the boot and the shaft on a boot inner side with respect to the projection is set larger than an interference between the boot and the shaft on a boot outer side with respect to the projection.
According to Patent Literature 6, two or more clamp mounting grooves are formed in an outer peripheral surface of a mounting portion of a boot, and boot mounting grooves are formed in a shaft at positions corresponding to the clamp mounting grooves. Under a state in which the clamp mounting grooves and the boot mounting grooves correspond to each other, fastening clamp corresponding to the number of clamp mounting grooves are mounted, thereby improving sealability.